Comparison of effects of vegetable oils blended with southern hemisphere fish oil and decontaminated northern hemisphere fish oil on growth performance, composition and gene expression in Atlantic salmon (Salmo salar L.)

Replacement of fish oil with sustainable alternatives, such as vegetable oil, in aquaculture diets has to be achieved without compromising the nutritional quality, in terms of n-3 highly unsaturated fatty acid (HUFA) content, of the product. This may be possible if the level of replacement is not too high and oil blends are chosen carefully but, if high levels of fish oil are substituted, a fish oil finishing diet prior to harvest would be required to restore n-3HUFA. However, a decontaminated fish oil would be required to avoid increasing undesirable contaminants. Here we test the hypotheses that blending of rapeseed and soybean oils with southern hemisphere fish oil will have a low impact upon tissue n-3HUFA levels, and that decontamination of fish oil will have no major effect on the nutritional quality of fish oil as a feed ingredient for Atlantic salmon. Salmon (initial weight ~ 0.8 kg) were fed for 10 weeks with diets in which 60% of fish oil was replaced with blends of soybean, rapeseed and southern hemisphere fish oil (SVO) or 100% decontaminated northern fish oil (DFO) in comparison with a standard northern fish oil diet (FO). Decontamination of the oil was a two-step procedure that included treatment with activated carbon followed by thin film deodorisation. Growth performance and feed efficiency were unaffected by either the SVO or DFO diets despite these having lower gross nutrient and fatty acid digestibilities than the FO diet. There were also no effects on the gross composition of the fish. Liver and, to a lesser extent flesh, lipid levels were lower in fish fed the SVO blends, due to lower proportions of neutral lipids, specifically triacylglycerol. Tissue lipid levels were not affected in fish fed the DFO diet. Reflecting the diet, flesh eicosapentaenoic acid (EPA) and total n-3 fatty acids were higher, and 18:1n-9 lower, in fish fed DFO than FO, whereas there were no differences in liver fatty acid compositions. Flesh EPA levels were only slightly reduced from about 6% to 5% although docosahexaenoic acid (DHA) was reduced more severely from around 13% to about 7% in fish fed the SVO diets. In contrast, the liver fatty acid compositions showed higher levels of n-3 HUFA, with DHA only reduced from 21% to about 18% and EPA increased from under 8% to 9–10% in fish fed the SVO diets. The evidence suggested that increased liver EPA (and arachidonic acid) was not simply retention, but also conversion of dietary 18:3n-3 and 18:2n-6. Increased HUFA synthesis was supported by increased hepatic expression of fatty acyl desaturases in fish fed the SVO diets. Flesh n-3HUFA levels and desaturase expression was significantly higher in fish fed soybean oil than in fish fed rapeseed oil. In conclusion, partial replacement of fish oil with blends of vegetable oils and southern hemisphere fish oil had minimal impact on HUFA levels in liver, but a greater effect on flesh HUFA levels. Despite lower apparent digestibility, decontamination of fish oil did not significantly impact its nutritional quality for salmon.     

The effect of fish and rapeseed oils on growth performance,egg fatty acid composition and offspring quality of sterlet sturgeon (Acipenser ruthenus)

The aim of this study was to evaluate the long‐term effects (7‐month experiment) of diets consisting of fish oil (Kilka fish) and vegetable oil (rapeseed) on the reproductive performance of sterlet sturgeon (Acipenser ruthenus) broodstock. Forty‐five broodstock (990.3 ± 20.05 g) were randomly allocated to three different diet treatments. Three experimental diets were formulated with graded levels of fish oil (100% FO), vegetable oil (100% VO), and a combination of fish and vegetable oil (50% FO + 50% VO). At the end of the 7‐month feeding trial period, the weight gain and final weight were changed significantly different between the treatments (p < 0.05). Broodstock fed the FO + VO diet had higher growth than those fed the only FO or VO diets (p < 0.05). The highest germinal vesicle migration percentage was observed in FO + VO treatment (p < 0.05). The DHA/EPA, DHA/ARA and EPA/ARA ratios in oocyte exhibited a significant difference in the different treatments (p < 0.05). This study indicates that nutrition of broodstock with diet including FO + VO (p < 0.05) can positively affect the growth performance of larvae compared with only FO or VO diets. Furthermore, the high levels of 18:1n‐9, AL and ALA contents in oocytes from broodstock fed VO and the lowest ALA content in oocytes from broodstock fed FO underlined the important role of broodstock diets in the reproductive process and embryonic and/or larval developments of sterlet.     

Effects of total replacement of fish oil by pork lard or rapeseed oil and recovery by a fish oil finishing diet on growth,health and fish quality of gibel carp (Carassius auratus gibelio)

An 84‐day growth trial was designed to investigate effects of dietary replacements fish oil with pork lard (PL) or rapeseed oil (RO) on growth and quality of gibel carp (Carassius auratus gibelio var. CAS III) (initial body weight: 158.2 ± 0.2 g), and responses of the fish refed fish oil (FO) diet. Three isonitrogenous (crude protein: 30%) and isolipid (crude lipid: 10%) diets were formulated containing 7.73% FO, PL or RO. Five experimental treatments including FO group (FO), PL group (PL), RO group (RO), group fed PL for 42 days and refed FO for 42 days (PL+rFO), RO and refed FO group (RO+rFO) was tested. At the end of first 42 days, the fish fed PL and RO had higher mortality than that of the control (P > 0.05). At the end of whole experiment, fish fed PL and RO showed higher plasma cortisol than FO fish (P < 0.05). RO+rFO fish showed higher lysozyme activity than RO fish (P < 0.05). Fish growth and feed utilization, composition of whole body and muscle, free amino acids, texture, off‐flavour substances or sensory attributes were not affected by dietary treatments (P > 0.05). PL and RO diet decreased muscle EPA, DHA and n‐3/n‐6 ratio (P < 0.05), while FO‐refeeding had recovery effect. It can be concluded that the replacement of FO by PL and RO does not affect the growth, feed utilization or fish tasting quality in gibel carp. Fish muscle fatty acids modified by dietary PL and RO can be recovered by refeeding with FO diet.     

The effect of total replacement of fish oil with DHA‐Gold® and plant oils on growth and fillet quality of rainbow trout (Oncorhynchus mykiss) fed a plant‐based diet

This study investigated the effect of the replacement of fish oil (FO) with DHA‐Gold (DHA‐G)‐supplemented plant oils (PO) in rainbow trout fed plant‐protein‐based diets. Five diets (450 mg g^?1 digestible protein and 150 mg g^?1 crude lipid) were fed to rainbow trout (initial weight 37 ± 0.5 g) for 12 weeks in a 15 °C recirculating water system. The lipid inclusion types and levels were FO, PO and PO with DHA‐G supplemented at 30 mg g^?1, 60 mg g^?1 or 90 mg g^?1 of the diet replacement for corn oil. Fish fed 90 mg g^?1 DHA‐G were significantly larger and consumed more feed than fish‐fed PO or FO (218 g and 2.6% bwd^?1 versus 181 g and 2.4% and 190 g and 2.3%, respectively). Feed conversion ratio was significantly increased in fish fed 90 mg g^?1 DHA‐G (0.99) as compared to fish‐fed FO (0.90) and 30 mg g^?1 DHA‐G (0.91). Panellists found trout fillets from fish fed the 90 mg g^?1 DHA‐G diet to have significantly fishier aroma and flavour than fish fed the FO diet. Fatty acid analysis demonstrated that 60 mg g^?1 or 90 mg g^?1 DHA‐G supplementation increased PO fed fish fillet DHA to fatty acid levels equivalent or higher than those fish fed a FO diet.     

Dietary lipid sources for seabream and seabass: growth performance, tissue composition and flesh quality

Due to its traditionally good availability, digestibility and high content of n ? 3 HUFA, fish oil is the main lipid source in fish feeds. However, world demand for this product has grown significantly in recent years, whereas its production, based on fisheries landings, is static. The purpose of the present study was to assess the effect of partial replacement of fish oil in compound diets for gilthead seabream and seabass, by several vegetable oil sources, on growth, dietary fatty acid utilization and flesh quality. Five iso‐energetic and isoproteic experimental diets were formulated (25% lipid content). Fish oil was the only added lipid source in the control (FO) diet, and it was included in the other experimental diets at a level high enough (40% of FO diet) to keep the n ? 3 HUFA levels well over 3% in order to cover the essential fatty acid requirements of these species. Fish oil was replaced by soyabean oil (SO), rapeseed oil (RO) and linseed oil (LO) or a mixture (Mix) of them. Feed intake in all dietary groups was in the range of results obtained for commercial diets in both species, and growth and feed utilization were very good. The results show that, providing a minimum content of essential fatty acids in the diet, it is possible to replace up to 60% of the fish oil by SO, LO and RO or a mixture of them in diets for seabream and seabass, without compromising fish growth. Fatty acid composition of liver and muscle reflected that of the diet, but utilization of dietary lipids differed between these two tissues and was also different for the different fatty acids. Despite reduction in dietary saturated fatty acids by the inclusion of vegetable oils, their levels in fish liver were as high as in fish fed the fish oil diet, whereas, in muscle, levels were reduced according to that in the diet. Linoleic and linolenic acids were accumulated in the liver proportionally to their levels in the diet, suggesting a lower oxidation of these fatty acids in comparison to other 18C fatty acids. Regarding eicosapentaenoic acid (20 : 5n ? 3; EPA), docosahexaenoic acid (22 : 6n ? 3; DHA) and arachidonic acid (20 : 4n ? 6; ARA), these essential fatty acids were reduced in the liver at a similar rate, whereas DHA was preferentially retained in the muscle in comparison with the other fatty acids, denoting a higher oxidation particularly of EPA, in the muscle. Some other PUFA increased despite their low dietary levels in seabream fed LO diets and in seabass fed SO diet, suggesting the stimulation of delta‐6 and delta‐5 desaturase activity in marine fish. Despite differences in fatty acid composition, fillet of fish fed vegetable oils was very well accepted by trained judges when assessed cooked.     

Effects of dietary vegetable oils and varying dietary EPA and DHA levels on intestinal lipid accumulations in Atlantic salmon

High dietary content of vegetable oil (VO) has been associated with increased intestinal lipid accumulations in fish. The extent of this in aquacultured Atlantic salmon (Salmo salar L.) and its health effects are not certain. Samples were therefore collected from two separate feeding trials to investigate the effect of high dietary VO on intestinal lipid accumulations in Atlantic salmon. In the first trial, the fish were fed diets high in plant protein and with fish oil or ~80% of the fish oil replaced with either olive oil, rapeseed oil or soybean oil in a land‐based experimental set‐up. The second trial was performed in sea cages under commercial production conditions, and the fish were fed two dietary concentrations of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (9.7% or 5.5% EPA + DHA of total fatty acids). Neither dietary VO nor variations in EPA and DHA led to any significant effects on intestinal health or lipid accumulations. There were, however, indications of a delayed lipid transport in the rapeseed oil‐fed fish of the first trial, possibly caused by high dietary ≥18‐carbon fatty acids and low dietary 16:0 fatty acid and cholesterol.     

Growth performance,feed utilization and product quality in slaughter size Atlantic salmon (Salmo salar L.) fed a diet with porcine blood meal,poultry oil and salmon oil

In a 17‐week experiment with Atlantic salmon (2.3–5.2 kg) in sea cages, a diet containing European animal by‐products and salmon oil (ABP) was compared with a control diet based on fish and plant ingredients, with respect to performance and product quality. Fish fed with the ABP diet had similar growth rates, but slightly improved feed conversion ratio (feed: gain; 1.08 versus 1.14) compared with the control. No differences were seen in fish length, live weight or condition factor. Final body composition was similar and retention of nitrogen and energy did not differ between diets. Higher DPA (C22:5 n‐3) content in the ABP diet apparently inhibited conversion of EPA (C20:5 n‐3) to DPA, resulting in higher EPA retention in muscle and whole body. Muscle and whole body DHA (C22:6 n‐3) level and n‐3 : n‐6 ratio were higher in the ABP group, corresponding with dietary levels. There were no differences in slaughter yield, quality classification, gaping score or fillet texture between diets. The feed with ABP contained less astaxanthin, possibly because of degradation catalyzed by iron in blood meal, and this resulted in lower muscle colour score and astaxanthin concentration (4.6 versus 6.4 mg kg⁻¹). A sensory test did not reveal any differences in odour, flavour, or texture.     

Effect of dietary fish and vegetable oil on the growth performance,body composition,fatty acids profile,reproductive performance and larval resistance in pearl gourami (Trichogaster leeri)

This study investigated the effect of two lipid sources on reproduction performance and growth in pearl gourami. For this purpose, 180 fish (3.32 ± 0.25 g) were fed with three isoenergetic (19.80) and isonitrogenous diets (480 g/kg protein) including FO (80 g/kg fish oil), FS (40 g/kg fish oil and 40 g/kg soybean oil) and SO (80 g/kg soybean oil) for 10 weeks before maturation. At the end of the trial, there was no significant difference in weight gain, feed conversation ratio and body composition between fish fed FO and FS diets. Individuals fed dietary FO had significantly higher levels of n‐3 long‐chain polyunsaturated fatty acids in the muscle (130.5 g/kg lipid) and ovary (140.4 g/kg lipid) as compared with those fed SO diet (64.5, 103.6 g/kg, respectively) (p < .05). Feeding pearl gourami with FO and FS diets enhanced regarding absolute fecundity, relative fecundity, the fertilization rate, larvae total length and survival at 3 day posthatch (p < .05). Also, 17 beta‐estradiol in plasma of fish fed dietary FO (6.2 ng/L) was higher than those fed SO diet (1.7 ng/L) (p < .05). In conclusion, we suggest FS diet for broodstock nutrition of pearl gourami as a model for asynchronous multi‐batch spawning fish.     

Effect of replacing dietary fish oil with soybean oil on growth performance,fatty acid composition and haematological parameters of juvenile meagre,Argyrosomus regius

A nutrition trial with meagre, Argyrosomus regius was assessed to determine the effect of dietary replacement of fish oil (FO) by soybean oil (SO) on the growth, feed utilization, body composition, fatty acid composition and basic haematological parameters. Six isonitrogenous (47% crude protein) and isoenergetic (gross energy 22 kJ/g) experimental diets were formulated by replacing 0 (FO), 20 (S20), 40 (S40), 60 (S60), 80 (S80) and 100 (S100) % of the FO with SO. Fish were fed three times daily to near satiation for 14 weeks. The specific growth rate (SGR) of fish fed S100 diet was significantly lower than the other treatments, except SO80 diet. The fish fed SO100 diet displayed significantly higher feed conversion ratio than that of other diets (P < 0.05). It was observed that fish fed the SO100 and SO80 diets displayed haemoglobin (HGB) levels significantly lower (P < 0.05) than fish fed the SO20 diet. Packed cell volume (PCV) of fish fed SO20 diet was significantly higher compared to SO100. The white blood cell (WBC) and red blood cell (RBC) remained unaffected by dietary treatment. The docosahexaenoic acid (22:6n‐3, DHA) and eicosapentaenoic acid (20:5n‐3, EPA) levels of meagre were significantly reduced by the substituting of dietary SO by FO at the end of the feeding period. The level of linoleic acid (18:2n‐6, LA) and linolenic acid (18:3n‐3, LNA) significantly raised in fish fed with SO diets (P < 0.05). The results of this study showed that SO could be replaced FO up to 80% in meagre diet without negative effect on growth performance and basic haematological parameters. Furthermore, the maximum level of FO replacement with SO determined by second order polynomial regression analysis, was 30.1% on the basis of maximum SGR.     

Alternative vegetable lipid sources in diets for grouper, Epinephelus coioides (Hamilton): effects on growth, and muscle and liver fatty acid composition

The aim of this study was to investigate the effects of different oils on growth performance and lipid metabolism of the grouper, Epinephelus coioides. Five experimental fish meal‐based isonitrogenous and isolipidic diets were formulated containing either 5.5%‐added fish oil (FO), soybean oil (SBO), corn oil (CO), sunflower oil (SFO) or peanut oil (PO). Each diet was fed to triplicate groups of 20 fish (initial body weight 13.2±0.02 g) grown in seawater at 28.0–30.5 °C for 8 weeks. Fish were fed twice a day to visual satiety. No significant differences in the survival, weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio or hepatosomatic index were found between fish fed the FO or vegetable oils (VO) diets. Dietary lipid sources did not affect whole‐body composition among grouper fed the various diets. Muscle of fish fed the FO diet had significantly higher levels of 14:0, 16:0, 16:1n‐7, 20:5n‐3[eicosapentaenoic acid (EPA)] and docosahexaenoic acid (DHA)+EPA (except for PO fed fish) compared with those of fish fed VO diets. However, the levels of 18:1n‐9, 18:2n‐6 and DHA/EPA ratios in the muscle of fish fed FO diet were significantly lower than those of fish fed the VO diets. The liver of fish fed the FO diet had significantly higher levels of 18:0, 20:5n‐3, 22:6n‐3, n‐3 highly unsaturated fatty acids and DHA+EPA than those of fish fed the VO diets, whereas increases in 18:1n‐9, 18:2n‐6 and mono‐unsaturated fatty acid levels were observed in the liver of fish fed the VO diets.     

Feeding Atlantic salmon diets with plant ingredients during the seawater phase – a full‐scale net production of marine protein with focus on biological performance,welfare, product quality and safety

By feeding Atlantic salmon diets with 64% of the fish oil (FO) replaced by vegetable oil, and with decreasing fishmeal (FM) inclusion levels from 213, 178 and 143 g kg⁻¹ (accumulated level during the seawater phase) in a full‐scale experiment producing 3.1 thousand tonnes fish, no significant negative effects on fish performance, health and product quality were observed. All dietary groups showed, however, moderate intestinal inflammation. Reduced growth and feed efficiency were seen with decreasing fishmeal inclusion levels. Two dietary groups demonstrated net marine protein production, while none of the groups showed net fish production (FIFO ≥1.65) due to the equal low FO inclusion. High plant oil level gave lower fillet level of persistent organic pollutants (POPs) compared with the levels surveyed on the Norwegian market. The study gave predictable incorporation rates of essential n‐3 long‐chain fatty acids in the fillet. Cooked salmon fillet from all dietary groups showed minor differences in sensory quality. Based on the present full‐scale production results, dietary FM inclusion down to 160 g kg⁻¹ (accumulated) during the seawater phase, concurrent to replacing ~70% of the FO with a suitable plant oil, is not regarded to represent any risk to fish performance, health or quality.     

Effects of different dietary lipid sources on growth performance,body composition and lipid metabolism‐related enzymes and genes of juvenile golden pompano,Trachinotus ovatus

Three groups of juvenile golden pompano, Trachinotus ovatus (54.75 ± 0.25 g), were each fed one of three diets containing different lipid sources: fish oil (FO), soybean oil (SO) and lard oil (LO). Fish were reared in sea cages for 8 weeks, and the fish fed the FO diet had significantly higher specific growth rate (SGR) but lower condition factor (CF) than the other treatments. The fatty acid (FA) composition of whole‐body lipids was closely correlated with those in the diets. Although no differences can be found in hepatic fatty acid synthase (fasn) activity, the carnitine palmitoyl transferase 1 (cpt1) activity in fish fed the FO diet was significantly higher compared with other treatments. In addition, the relative gene expression of lipid metabolism‐related enzymes, such as cpt1, fas, apolipoprotein B100 (apoB100), delta‐6 fatty acyl desaturase (fadsd6) and fatty acid‐binding protein 1 (fabp1), was also influenced by the different dietary lipid sources. Serum triglyceride (TG) and glucose content in fish fed the LO and FO diets were significantly higher than those in the SO group. Accordingly, it can be concluded that FO could not be completely replaced by SO or LO in golden pompano diets. The lipid sources of a diet could impose significant influence on body condition factor and hepatic lipid metabolism of golden pompano.     

First step of non‐fish meal,non‐fish oil diet development for red seabream, (Pagrus major), with plant protein sources and microalgae Schizochytrium sp

A feeding experiment was conducted to develop non‐fish meal and non‐fish oil diet for red seabream by using plant protein source and Schizochytrium meal which is rich in 22:6n‐3 (DHA). Three iso‐nitrogenous and iso‐lipidic experimental diets were prepared (CP 41.2% ± 0.4%, CL 16.4% ± 1%). Control diet contained both fish meal (40%) and fish oil (6%). In the second diet, fish meal was replaced by plant meals (soy protein concentrate, soybean meal, corn gluten meal) [FO]. In the third diet, fish meal and fish oil were replaced by algae meal (Schizochytrium sp. powder) and plant proteins [AO]. Duplicated groups of juvenile red seabream (8.8 g ± 1.5) were fed the experimental diets for 12 weeks to near satiation. There was no statistical difference among treatment in specific growth rate. Feed conversion ratio of AO diet group was higher than that of control. In wet basis, whole body protein level was significantly higher in AO diet than FO group while lipid content was lower than control group. In fatty acid profile, AO group had significantly lower 18:4n‐3, 20:4n‐3, 22:5n‐3 and 20:5n‐3 (EPA) level, but significantly higher 18:3n‐3 and DHA level than the other two diet fed fish. The results might suggest that further developments in microalgae diet offer a promising lipid source of n‐3 PUFA as essential fatty acid on marine fish. And it showed possibility to develop non‐fish meal and non‐fish oil feed for marine aquaculture fish by using microalgae.     

Fish proteins not lipids are the major nutrients limiting the use of vegetable ingredients in catfish nutrition

The objective of this study was to determine the major nutrient limiting growth and lipid metabolism in African catfish fed diets composed of vegetable ingredients. Four diets were formulated from contrasted meal (fish meal: FM; vegetable meal: VM) and oil (fish oil: FO; vegetable oil: VO) sources. Replacement of FO by VO did not affect specific growth rate (SGR) and feed efficiency, whereas lower values were recorded in the case of FM replacement. LC‐PUFAs muscle contents were higher in fish fed control FMFO diet than in fish fed vegetable ingredients. However, the decrease in docosahexaenoic acid (DHA) concentration in FMVO group was limited compared to VM groups despite the same low DHA level in those three diets. These results may suggest an activation of LC‐PUFA biosynthesis from PUFA precursors brought with vegetable oils in FMVO group. This hypothesize is reinforced by the significant stimulation of elovl5 gene expression in liver and intestine from fish fed FMVO. Therefore, this study demonstrated that African catfish is able to bioconvert LC‐PUFAs at a significant biological level when FO is replaced by VO whereas the use of plant proteins has strong detrimental effects on growth performances.     

Effects of alternative dietary oils on lipid metabolism and related gene expression in hybrid grouper (♀Epinephelus fuscoguttatus × ♂E. lanceolatu)

An 8‐week growth trial was conducted to evaluate effects of dietary oil sources on growth, enzymes activity and genes expression levels related to lipid metabolism of hybrid grouper (♀Epinephelus fuscoguttatus × ♂E. lanceolatu) juveniles. Seven iso‐lipid (97 g/kg of dry matter) and iso‐protein (503.5 g/kg of dry matter) experimental diets were formulated containing 50 g/kg fish oil (FO; acting as controls) or various vegetable oils (VOs): corn oil (CO), sunflower oil (SO), tea oil (TO), olive oil (OO), rice oil (RO) and mixed oil (MO; comprising equal amounts of these oils). Each diet was fed to triplicate groups of 40 fish for per repetition (15.09 ± 0.01 g) for 56 days. The results show that (a) alternative dietary oils had no significant effects on final weight compared with control group (p > .05); (b) compared with FO group, VOs significantly changed the contents of serum lipoproteins, cholesterol, triglycerides and the activity of liver lipid‐metabolizing enzymes (p < .05); (c) CO group had the least effect on the serum lipoproteins, triglycerides and cholesterol of grouper compared with control; the activity of liver lipid‐metabolizing enzymes in RO and control group was the closest; (d) the mRNA levels of Δ6 Fatty acid desaturase (Δ6Fad), hormone‐sensitive lipase (HSL) and lipoprotein lipase (LPL) were not significantly effected by lipid sources, but CO, TO, OO and MO significantly down‐regulated the expression of fatty acid synthetase (FAS) mRNA level in liver, while RO opposite (p < .05); (e) vegetable oil significantly up‐regulated peroxisome proliferator‐activated receptor α (PPARα) and peroxisome proliferator‐activated receptor β (PPARβ) mRNA levels, while TO and RO down‐regulated peroxisome proliferator‐activated receptor γ (PPARγ) mRNA levels (p < .05); and 6) MO significantly increased the mRNA levels of heart‐type fatty acid‐binding protein (H‐FABP) and adipocyte‐type fatty acid‐binding protein (A‐FABP) (p < .05), while other VOs had no effect on them (p > .05). In conclusion, dietary substitution of FO by VO in diet affected lipid metabolism of grouper, which may be regulated by PPARs.     

Non‐fish meal,non‐fish oil diet development for red sea bream,Pagrus major,with plant protein and graded levels of Schizochytrium sp.: Effect on growth and fatty acid composition

A feeding experiment was conducted to determine the optimal formulation level of algae meal, which is rich in docosahexaenoic acid (DHA), in a non‐fish meal diet. Six iso‐nitrogenous (450 g/kg) and iso‐lipidic (130 g/kg) experimental diets were prepared. The control diet was formulated with fish meal (400 g/kg), fish oil (60 g/kg), plant protein sources (220 g/kg) and rapeseed oil (50 g/kg). Plant protein sources (soy protein concentrate, soybean meal and corn gluten meal), rapeseed and fish oil were formulated in the second diet (NFM + FO). In the third diet, fish oil of the NFM + FO diet was replaced by rapeseed oil (NFM + NFO) and designated as the negative control. In the other three diets, rapeseed oil in the NFM + NFO diet was replaced with algae meal (Schizochytrium sp. powder) at 50 g/kg, 100 g/kg and 150 g/kg (AM5, AM10 and AM15, respectively). Triplicate groups of juvenile red sea bream (8.8 g) were fed the experimental diets for 12 weeks near satiation. The growth was lowest in the fish fed NFM + NFO diet. This was improved by the formulation of algae meal, which reached the growth level of the NFM + FO group in the AM10 group. The lipid content of the whole fish body in the NFM + NFO group was significantly lower than those of other groups. The fatty acid profile showed significant differences among dietary treatments. DHA content in total and polar lipids of the whole body and liver was highest in the AM10 and AM15 groups. These results reconfirm that microalgae are a suitable lipid source for the replacement of dietary fish oil for marine fish, and the optimal level was estimated as 50 g/kg?100 g/kg in diet.     

Inter-individual variation in total fatty acid compositions of flesh of Atlantic salmon smolts-fed diets containing fish oil or vegetable oil

Fish such as Atlantic salmon (Salmo salar L.) are a natural source of n‐3 highly unsaturated fatty acids (HUFA) eicosapentaenate (EPA; 20:5n‐3) and docosahexaenoate (DHA; 22:6n‐3), which are essential for protecting humans against cardiovascular diseases. Thus, flesh n‐3 HUFA level is a trait of considerable importance in farmed fish, particularly now that the fishmeal and fish oil (FO) components of traditional aquaculture diets have to be replaced by more sustainable alternatives including plant meals and vegetable oils (VO). The present study aimed to characterize the inter‐individual variation in this trait in a single strain of Atlantic salmon. Fish were grown for 12 weeks on either an FO diet, or a diet with 100% of the FO replaced by a VO blend containing rapeseed, linseed and palm oils, flesh n‐3 HUFA content and composition determined, and the variation between individuals characterized. The results showed that, irrespective of diet, variation exists in the content of n‐3 HUFA in the flesh of individual salmon, showing that individual animals can display an enhanced ability to maintain high levels of n‐3 HUFA in their flesh. The pros and cons of defining the trait on a qualitative or quantitative basis are discussed.